HMS C21

HMS C21 was one of 38 C-class submarines built for the Royal Navy in the first decade of the 20th century. The boat survived the First World War and was sold for scrap in 1921.

Design and description
The C-class boats of the 1907–08 and subsequent Naval Programmes were modified to improve their speed, both above and below the surface. The submarine had a length of 142 ft overall, a beam of 13 ft and a mean draft of 11 ft. They displaced 290 LT on the surface and 320 LT submerged. The C-class submarines had a crew of two officers and fourteen ratings.

For surface running, the boats were powered by a single 12-cylinder 600 bhp Vickers petrol engine that drove one propeller shaft. When submerged the propeller was driven by a 300 hp electric motor. They could reach 13 kn on the surface and 8 kn underwater. On the surface, the C class had a range of 910 nmi at 12 kn.

The boats were armed with two 18-inch (45 cm) torpedo tubes in the bow. They could carry a pair of reload torpedoes, but generally did not as they would have to remove an equal weight of fuel in compensation.

Construction and career
C21 was laid down on 4 February 1908 by Vickers at their Barrow-in-Furness shipyard, launched on 26 September and was completed on 18 May 1909. During World War I, the boat was generally used for coastal defence and training in home waters. C21 was sold for scrap on 5 December 1921.